Spring Doctor

ABSTRACT

A spring doctor, particularly for use for cleaning the surface of rolls ( 2 ), used in the and including a blade ( 8 ) that is essentially the width of the roll ( 2 ) being cleaned, and which is attached to a blade holder ( 1 ). In the device, there are operating means (for example,  6, 7 ) for creating the desired pressure of the doctor blade against the roll. Longitudinally, the blade ( 8 ) is curved for at least part of its length.

The present invention relates to a spring doctor, and more specificallyto a doctor, which is used to scrape clean the various rolls of amachine used in the manufacture of paper.

The usual construction and positioning of doctors are such that thedoctor blade, which is usually in the order of 75-85 mm-long and of thedesired width, i.e. essentially the same width as the roll beingdoctored, rests with a specific force against the surface of the rolland cleans the surface of fibres and other materials adhering to it.Though the angle of contact of the blade relative to the surface of theroll is often in the order of 25 degrees when the blade is new, theangle of contact changes as the blade wears, so that the angle can be inthe order of 35 degrees before the blade is replaced with a new one.

Before replacement, the length of present doctor blades is about 60 mm.Wear causes the surface pressure of the blade to change according to it.In practice, it has also been noted that when using existing types ofblade construction there is very little possibility to increase the wearmargin/length of the blade, as this will lead to problems arising fromthe deflection of the blade. Similar problems also arise if the pressureof the blade is increased, when the point of the blade will open andwill no longer closely follow the surface of the roll. This results in apoorer doctoring result.

The deficiencies of blades according to the prior art also lead tovarious compromises being made in the manufacture of blades, theavoidance of which would improve the quality of the blades beingmanufactured.

Doctor blades are changed in paper machines at approximately weeklyintervals. The change as such is not a difficult operation, but it isexpensive, as it takes about one hour and costs can easily rise to aboutε20,000. Thus, a lengthening of the interval between changes wouldeasily have even considerable financial effects in the manufacture ofpaper.

The present invention is intended to create a new, improved doctor-bladeconstruction, with the aid of which the drawbacks besetting the priorart can be avoided and savings will become possible in the manufactureof paper.

These and other benefits and advantages of the invention are achieved inthe manner stated to be characteristic in the accompanying Claims.

In the following, the invention is examined in greater detail withreference to the accompanying schematic drawings, which show oneembodiment according to the invention. Thus

FIG. 1 shows one blade carrier, blade holder, and blade according to theinvention, when the blade is at its full size, and

FIG. 2 shows the same construction in a situation, in which the bladehas worn more or less to a state in which it must be replaced.

The roll, the surface of which is cleaned by the doctor blade, in markedin the figures with the reference number 2. As can be seen, the presentcase concerns a roll 2 with a relatively large diameter, the surface ofwhich is only slightly curved in the figures.

The blade holder 1 has a more or less conventional construction. It isformed of a frame structure, which is permanently attached, for example,to the frame structure of the paper machine. The frame 5 of the bladeholder 1 has a lug 3 for a shaft 4. The blade holder 1 is pivoted aroundthe shaft 4, allowing the blade holder to be rotated to a limited extentaround the shaft 4 according to the control. The control is, in turn,provided by using hose-like components 6 and 7, filled with a pressuremedium, which act on the blade holder to rotate it in differentdirections, as they are located on different sides of the pivot. Thehoses 6 and 7 are supported between the body 5 and a suitable surface ofthe blade holder.

It should be noted that there are numerous different models of knownblade holders on the market. The invention is thus not limited to theblade holder shown by way of example.

The actual doctor blade 8 is attached and suitable supported on the sideof the blade holder 1 facing the roll. The attachment is made in aconventional manner, with the aid of a loading plate 9 and acounter-plate 10.

The blade construction 11 according to the prior art is shown by abroken line in FIG. 1. In practice, this means that the doctor blade 11is shorter than the blade according to the invention. The bladeaccording to the prior art is also of a straight construction.

Instead of using a straight construction, the blade construction 8according to the invention is made to be curved, which also means thatthe construction is made sturdy, compared to the doctor blade accordingto the prior art. Thanks to the non-buckling and essentiallynon-deflecting construction achieved, the doctor blade can be madeclearly longer than a blade according to the prior art, which in turnmeans that replacement will be needed much less frequently than whenusing a traditional doctor blade. The savings will be considerable.

The construction according to the invention also achieves anotheradvantage, which is that, by curving the doctor blade 8 as shown, andbending it slightly upwards, as shown by the reference number 12, theangle of the blade relative to the surface 2 of the roll can be made toremain nearly constant over the entire operating life of the blade. Thisalso brings savings, as separate measures are not required to adjust theangle. Similarly, the doctoring situation remains constant for theentire operating life of the doctor, because the angle, the contactsurface, and the pressure will not change.

A protector plate suitable for the purpose can be attached behind theblade and will prevent dirt that may accumulate on the back of the bladefrom entering the blade holder. FIG. 1 shows an example of such aprotector plate, marked with the reference number 13. In particular,cleanliness is an extremely important factor in the inside of ahose-loaded holder. If solid dirt gets between the loading hose and theloading plate, it will cause a deviation in the loading profile of theblade. This will lead to uneven blade wear, a reduction in doctoringeffect, possible entry of dirt into the paper, a deterioration in themoisture profile of the paper and, at the very least, a reduction in theproduction efficiency of the paper machine, due to web breaks.

As stated above, the improvements in the doctor blade according to theinvention bring considerable savings, because the use of thisconstruction minimizes the operations that cause detriments toproduction. The increases in the manufacture of the actual blade, and inthe subsequent costs are only very small.

The invention is described above with reference to only one wellregarded embodiment, which must be considered as in no way restrictingthe invention.

Thus, the blade according to the invention shown in the figures can beadapted in many ways. For example, instead of the blade being curvedover its entire length, it can also be made as a combination with acurved portion and also a straight portion. A blade curved in twodirections is also possible. The radius of the curve can also be changedas desired over the length of the blade. It may also be sensible to makethe blade with a varying thickness. Such an alternative, in which theblade thins towards its point may be particularly suitable.

Blades like that shown are usually manufactured from a compositematerial, which, in other words, is usually formed of a plastic-basedmatrix, to which reinforcement is added. The reinforcement is normallyof a fibrous material; aramid fibres, carbon fibres, kevlar, or similar.The invention also permits the desired elasticity properties andstiffness to be achieved by altering the amount and orientation of thereinforcement. In other words, if desired, the properties can be alteredby arranging more fibres in one part of the blade than in another, whilesimilarly the fibres can be oriented in one direction or another inspecific parts of the blade.

The shape and construction of the blade holder shown in the figures byway of example can differ even greatly from the model shown. Theinvention is in no way restricted to the solution shown. It is alsoself-evident that the pressure, exerted by the blade on the roll beingdoctored, can by created in any way at all. The means for creating thepressure need be in no way connected to the blade holder. For example,the pressure can be regulated by a microprocessor and be variable forthe entire duration of the operation.

1. A spring doctor for cleaning the rolls of a paper machine duringoperation comprising: a blade that is essentially the width of a rollbeing cleaned, and which is attached to a blade holder; and operatingmeans for creating a desired pressure of said blade against the roll,wherein said blade is manufactured from a composite material formed of amatrix and a reinforcement, in which the reinforcement is formed of afibrous material and that, in operation, said blade is convex in adirection outwards from the roll.
 2. A spring doctor according to claim1, wherein the blade holder is pivoted around a shaft pin, to be able tobe rotated to at least a limited extent.
 3. A spring doctor according toclaim 1, wherein said blade has, at a distance from its point, aplate-like dirt protector.
 4. A spring doctor according to claim 1,wherein said blade has, in an immediate vicinity of an attachmentlocation of the blade holder, a bend, curve, or other similar shape. 5.A spring doctor according to claim 1, wherein said blade is acombination of a curved portion and an essentially straight portion. 6.A spring doctor according to claim 1, wherein a thickness of said bladevaries over its length.
 7. A spring doctor according to claim 6, whereinsaid blade thins towards its point.
 8. A spring doctor according toclaim 1, wherein a number or orientation of the reinforcing fibres ofthe composite material of said blade varies in different parts of saidblade.